code: def onBars(self, bars):
      vwap = self.__vwap[-1]
      if vwap is None:
          return
  
      price = bars[self.__instrument].getClose()
      if price > vwap * (1 + self.__buyThreshold):
          self._buySignal(price)
      elif price < vwap * (1 - self.__sellThreshold):
          self._sellSignal(price)
  
file_path: pyalgotrade/samples/bccharts_example_2.py
imports: from pyalgotrade import bar
  from pyalgotrade import strategy
  from pyalgotrade import plotter
  from pyalgotrade.technical import vwap
  from pyalgotrade.barfeed import csvfeed
  from pyalgotrade.bitstamp import broker
  from pyalgotrade import broker
label_desc: Use image node_id 7 for calling the VWAPMomentum obj's underlying member method code with example usage: obj.onBars(bars) without return types